FIG. 1 shows a simple schematic of a field-commutated motor 10 powered by a power supply 12, and having a stator 16 and a rotor 20. The stator mounts excitation coils 17 (A-A', B-B', C-C' and D-D'), which are sequentially excited such that the coils act as magnets, having north and south poles, to generate forces on the permanent magnets 21 mounted on the rotor 20, thereby rotating the rotor 20. A knowledge of the position of the rotor magnets 21 relative to the coils 17 is necessary for the coils to be excited in the proper sequence and with the proper timing to provide the desired torque, speed or direction of rotation of the rotor 20. Typically, a sensor 22 provides raw data representative of the rotor angular position in a "sensor", or uncalibrated, coordinate system. However, this data must be used to determine the position of the magnets 21 relative to the coils 17. Initialization of the motor, as used herein, refers to determining the relationship between the uncalibrated coordinate system and a coordinate system having a known relationship to the excitation coils 17, such that the relationship of the magnets 21 to the coils can be determined from the raw, or uncalibrated, angular data. The raw data is initialized and the initialized data is used in sequencing and timing the excitation of the coils 17.
Initialization of the motor 10 can be rather straightforward if the motor 10 is accessible and not under load. Excitation of the stator 16 with a test voltage of a known orientation produces a known angular position of the rotor 20, because the load angle is zero. The raw data from the sensor 22, giving an angle in the uncalibrated coordinate system, can be related to a q-d rotor coordinate system, where d is the axis of the magnets 21 and q is the quadrature axis, such that the "error angle" between the uncalibrated and rotor coordinate system is determined. As the relationship between the q-d rotor coordinate system and the excitation coils 17 is known, the error angle is then used during operation of the motor to properly excite the coils 17 to obtain the desired performance of the motor 10. Accordingly, initialization is not necessarily a difficult problem at the motor factory.
However, initialization as above requires that motors shipped from the factory include the sensor 22 and be subsequently carefully handled such that the physical relationship between the sensor 22 and rotor 20 is not disturbed. Such motors are often installed in complex machinery, such as elevators, at the site where the machinery is to be installed. Installation provides yet another opportunity for the initialization to be disturbed. Initialization, or re initialization, of an installed motor is tedious. The motor 10 is typically under load, and the load (e.g., the elevator) must be manually manipulated, such as by adjusting cables, to remove the load to allow the initialization procedure outlined above to be followed. Such manipulation can be time consuming and require additional personnel. Replacement in the field of a failed sensor 22 similarly requires removal of the load or installation of a new initialized motor including a new sensor 22. A simpler and more efficient initialization procedure would represent a useful advance in the art.
Accordingly, it is an object of the present invention to address one or more of the aforementioned deficiencies and disadvantages of the prior art.
Other objects will in part appear hereinafter and in part be apparent to one of ordinary skill in light of the disclosure herein.